Gear selection and engagement device for a motor vehicle transmission

Abstract

 Gear selection and engagement device for a motor vehicle transmission, the said device comprising a shaft (2) moving in the direction of and round its own axis and constituting a support for a number of hubs (4, 5, 6) each integral with a corresponding fork (1) the said device also comprising a first set of teeth (8, 9, 10, 11) projecting radially from the said shaft (2) and being axially and torsionally integral with the same, one of the said hubs (4, 5, 6) being arranged between two adjacent teeth on the said first set; the said device also comprising a second set of teeth (16, 17, 18, 19, 20) projecting radially from the said shaft (2) being torsionally integral with it and being axially fixed in relation to the transmission case; each of the said hubs (4, 5, 6) having at least one pair of axial grooves (25) designed to accommodate the teeth in the said first and second set; the said grooves (25) being arranged round the circumference of each hub in such a preset manner that, for a preset angular position of the said shaft (2) corresponding to a preset gear selection, all the teeth in the first set (8-11) are aligned axially with corresponding grooves (25) on the said hubs with the exception of the teeth adjacent to a preset hub belonging to the fork which must be shifted axially for engaging the said gear.

Description

[0001] The present invention relates to a gear selection and engagement device designed for assembly on a motor vehicle transmission of the type comprising a number of gears moved axially by corresponding control forks, each of the said gears being designed to be moved into such a position as to mesh with another axially-fixed gear, so as to form a gear pair with a preset transmission ratio. one aim of the present invention is to provide a gear selection and engagement device for use on the abovemention ed type of transmission, the said device comprising a sin gle moving control shaft designed to shift the said forks which are needed for both gear selection and engagement. Another aim of the present invention is to provide a device of the abovementioned type designed to control a large number of forks and, therefore, employable on trans missions with a particularly large number of gears, e.g. the transmission on an industrial vehicle. A further aim of the present invention is to provide a highly compact device ensuring smooth, reliable operation.

[0002] With these aims in view, the present invention relates to a gear selection and engagement device for a motor vehicle transmission comprising a number of axially-moving gears, each designed to be moved into such a position as to mesh with another axially-fixed gear so as to form a gear pair with a preset transmission ratio, the said axially-moving gears being controlled by corresponding axially-moving control forks, characterised by the fact that the said device comprises a shaft moving in the direction of and round its own axis in relation to the transmission case by means of manually-operated control means, the said shaft constituting a support for a number of hubs each integral with a corresponding fork; a first set of teeth projecting radially from the said shaft and being axially and torsionally integral with the same and one of the said hubs being arranged between two adjacent teeth on the said first set; a second set of teeth projecting radially from the said shaft, being tor sionally integral with it and axially fixed in relation to the said case and one of the said hubs being arranged between two adjacent teeth on the said second set; each- of the said hubs having at least one pair of axial grooves designed to accommodate teeth on the said first and second sets when the said shaft is shifted axially by the said control means so as to prevent the relative hubs from moving as a consequence of the said axial displacement; the said grooves being arranged round the circumference of each hub in such a preset manner that, for a preset angular position of the said shaft corresponding to a preset gear selection, all the teeth in the first set are aligned axially with corresponding grooves on the said hubs, with the exception of the teeth adjacent to a preset hub belonging to the fork which must be shifted axially for engaging the said preset gear, so that, following subsequent axial displacement of the said shaft, only the said hub preset for engaging the said gear is shifted axially by one of the said adjacent teeth in the said first set; with the said shaft in the said angular position, the second set teeth adjacent to the said preset hub being aligned with the corresponding grooves on the hub and all the other said second set teeth being arranged essentially contacting the other hubs, so as to prevent the said hubs from moving axially during axial displacement of the said hub selected for engaging the said gear.

[0003] one arrangement of the present invention will now be described, by way of a non-limiting example, with reference to the attached drawings in which :

- Fig.1 shows a view in perspective of the gear selection and engagement device according to the present invention;

- Fig.2 shows a side view of the device;

- Fig.3 shows a cross section of the Fig.2 device along line III-III;

- Fig.4 shows an axial longitudinal section of the device;

- Fig.s 5 and 6 show two cross sections of the device, as in Fig.4, but in two different operating positions corres ponding to the engagement of two different gears.

[0004] The device covered by the present invention is designed for use on a motor vehicle transmission (not shown) comprising a number of axially-moving gears, each designed to be moved by a corresponding fork (₁) into such a position as to mesh with another axially-fixed gear, so as to form a gear pair with a preset transmission ratio. In the arrangement shown, the device is privided with three such forks designed to shift corresponding gears axially in two opposite directions.

[0005] The device comprises a shaft (2) moving in the direction of and round its own axis in relation to the transmission case. For such a purpose, as shown in Fig.2, the end sections (2a, 2b) of the said shaft are housed in correspond ing bearings of walls 3 on the said case. Shaft ₂ constitutes a support for a number of hubs (4, ₅, 6) each integral with a corresponding fork (₁) as shown clearly in Fig._l. The said hubs are thus free to move axially and to turn in relation to the centre part (7) of shaft ₂, the said centre part (7) being greater in diameter than end sections ₂a and ₂b on the shaft.

[0006] The device also comprises a first set of teeth projecting radially from shaft 2 and both axially and torsionally integral with it. The said teeth are arranged on the shaft so that one of hubs 4, 5 or 6 fits between two adjacent teeth. Consequently, in the arrangement shown, which provides for only three hubs, the teeth are four in number (8, 9, 10, 11) as shown clearly in the Fig.₄ section. For conveniently forming the said teeth, provision is made for key ₁4 housed inside a corresponding annular groove (₁₅) in the centre part (7) of shaft 2. The said teeth project from the same side of the said key the base section of which is housed in the said groove.

[0007] The device also comprises a second set of teeth also pro jecting radially from the centre part (7) of shaft 2 and being torsionally integral with the shaft and fixed axially in relation to the transmission case. As on the first set of teeth, one of hubs 4, 5 or 6 is arranged between two adjacent teeth on the said second set. In the arrangement shown, the said radial teeth are five in number (16, 17, 18, 19, 20) as shown clearly in the Fig.4 section. As in the case of the first set, the teeth in the said second set may also be formed by means of a key (21) also housed in a corresponding longitudinal groove (2₂) on the centre part (7) of shaft ₂, the said teeth projecting from one side of the key and the base section of the latter being housed in the said groove.

[0008] To fix the teeth in the said second set axially in relation to the transmission case, end teeth 16 and 2₀ of key ₂₁ rest against the surfaces of case 3, whereas, to enable axial movement of shaft ₂ in relation to the key, which is fixed axially, the latter is allowed to slide inside the corresponding groove 2₂.

[0009] Each hub 4, 5 and 6 is provided with at least one pair of axial grooves (₂₅) each designed to accommodate, in the manner described hereafter, teeth in both the first and second set, when shaft ₂ is displaced axially. Axial displacement and rotation of shaft 2 are controlled by control means, indicated as a whole by number ₂6, and comprising a first bushing (27), integral with shaft 2, and a second bushing (₂8), integral with a control bar (₂9) arranged essentially perpendicular to shaft 2. The said two bushings are connected by means of an essential ly spherical coupling (30) comprising a head (3₁) integral with bushing 28 and connected between a pair of tabs (3₂) integral with bushing 27. The side surfaces of the said head are conveniently cylindrical and designed to rest on corresponding flat surfaces of tabs 32. Furthermore, a pin (33) (Fig.₁) inserted inside the tabs fits through a slot (34) on head 31. Obviously, therefore, with such a construction arrangement, each rotation of control bar 29 round its own axis is accompanied by axial traversing of shaft 2, whereas, traversing of the said bar is accompanied by rotation of the said shaft. Grooves ₂₅ on each hub ₄, ₅ and 6 are arranged round the circumference of the relative hub in such a preset manner that, for a preset angular position of shaft ₂ corresponding to a preset gear selection, all the teeth in the first set are essentially aligned with corresponding grooves on the said hubs, with the exception of the teeth adjacent to a preset hub belonging to the fork which must be displaced axially for engaging the said preset gear. In the arrangement shown, for the preset angular position of shaft ₂ shown in Fig.4, each of hubs-5 and 6 is provided on opposite sides of each with a pair of grooves (25) designed to align with teeth 9, 10 and 11, as shown clearly in Fig.₄, whereas no groove is provided on hub 4 for aligning with teeth 8 and 9.

[0010] Grooves 2₅ on each hub are arranged in such a manner that, with shaft ₂ in the abovementioned angular position, the teeth in the second set are aligned with corresponding grooves (₂₅) on the only hub to be displaced for engaging the preset gear, whereas all the other teeth in the said second set are arranged essentially contacting the other hubs, so as to prevent axial displacement of the said hubs during axial displacement, in the manner hereafter described, of the said preset hub. Consequent ly, in the arrangement shown in Fig.4 and for the angular position of shaft ₂ shown in the said Figure, grooves ₂₅ are provided only on hub ₄ in alignment with teeth ₁6 and ₁7 in the second set, whereas no groove ₂₅ is provided on the other hubs (₅, 6) in alignment with the other teeth (18, 19, 20) in the said second set.

[0011] Clearly, the arrangement of grooves ₂₅ on the hubs depends on the displacement envisaged for fork ₁ and will become clearer from the following examination of the way in which the device operates.

[0012] With reference to Fig.₄ showing the device covered by the present invention with none of the gears engaged, assume a gear engagement is required, such engagement being performed by shifting rightwards, in Fig.4, fork ₁ on the left of the drawing. Axial traversing of control bar 29, which turns bushing ₂₇ and, consequently, also shaft 2, moves shaft ₂ into the angular position shown in Fig.₄ in which teeth 9, 10 and 1₁ in the first set are aligned with corresponding grooves ₂₅ on hubs 5 and 6. Axial displacement of the control bar thus serves to select a preset gear.

[0013] In the abovementioned preset gear selection arrangement, teeth 18, 19 and 20 in the second set are arranged essentially on each side of hubs ₅ and 6, thus locking them axially and preventing any displacement during the following engagement operation. The latter is achieved by turning control bar 29 which is accompanied by axial traversing of bushing 27 and, consequently, also of shaft 2. If such rotation is anticlockwise in Fig.4, it is accompanied by rightward displacement (Fig.4) of the shaft (Fig.5) during which tooth 8 shifts hub 4 in the same direction, whereas teeth 9 and 10 simply fit into the corresponding grooves (25) on respective hubs 5 and 6. Clearly, therefore, during such displacement, corresponding to actual engagement of one of the gears, only the hub involved in the said engagement is displaced while the others are locked in the idle position by the teeth in the second set.

[0014] If another gear is to be engaged, however, such engagement being achieved by shifting leftwards fork 1 on the left of Fig.4, the selection arrangement is the same as that already described whereas, for engaging the gear, control bar 29 is turned clockwise in Fig.4 so as to shift shaft 2 and, consequently, also hub 4 leftwards in Fig.4.

[0015] This new engagement set-up is shown in Fig.6. As this clearly shows, during such displacement, teeth ₁₀ and 11 in the first set fit into corresponding grooves 25 on corresponding hubs ₅ and 6 which are locked firmly in the idle position by the teeth in the second set.

[0016] A different gear selection may be achieved by turning shaft 2 into an angular position other than the one already described. This new position may correspond to such a preset arrangement of grooves ₂₅ on the three hubs (4, 5, 6) as to determine, following axial displace ment of the shaft, axial displacement of another fork in a preset direction or the simultaneous displacement of two of the said forks.

[0017] Obviously, by providing each hub (4, ₅, 6) with an appropriate number of grooves (2₅), the axial displacement of one or more hubs may be controlled while, at the same time, locking the others axially.

[0018] To those skilled in the art it will be clear that changes can be made to the arrangement described of the present invention, both in terms of form and arrangement of the various parts involved, without, however, departing from the scope of the present invention.

Claims

₁) - Gear selection and engagement device for a motor vehicle transmission comprising a number of axially-moving gears, each designed to be moved into such a po sition as to mesh with another axially-fixed gear so as to form a gear pair with a preset transmission ratio, the said axially-moving gears being controlled by corres ponding axially-moving control forks, characterised by the fact that the said device comprises a shaft moving in the direction of and round its own axis in relation to the transmission case by means of manually-operated control means, the said shaft constituting a support for a number of hubs each integral with a corresponding fork; a first set of teeth projecting radially from the said shaft and being axially and torsionally integral with the same and one of the said hubs being arranged between two adjacent teeth on the said first set; a second set of teeth projecting radially from the said shaft, being torsionally integral with it and axially fixed in relation to the said case and one of the said hubs being arranged between two adjacent teeth on the said second set; each of the said hubs having at least one pair of axial grooves designed to accommodate teeth on the said first and second sets when the said shaft is shifted axially by the said control means so as to prevent the relative hubs from moving as a consequence of the said axial displacement; the said grooves being arranged round the circumference of each hub in such a preset manner that, for a preset angular position of the said shaft corresponding to a preset gear selection, all the teeth in the first set are aligned axially with corresponding grooves on the said hubs, with the exception of the teeth adjacent to a preset hub belonging to the fork which must be shifted axially for engaging the said preset gear, so that, following subsequent axial displacement of the said shaft, only the said hub preset for engaging the said gear is shifted axially by one of the said adjacent teeth in the said first set; with the said shaft in the said angular position, the second set teeth adjacent to the said preset hub being aligned with the corresponding grooves on the hub and all the other said second set teeth being arranged essentially contacting the other hubs, so as to prevent the said hubs from moving axially during axial displacement of the said hub selected for engaging the said gear.

₂) - Device according to Claim ₁, characterised by the fact that the said teeth in the said first set are formed on a key inserted inside a first axial groove on the said shaft.

3) - Device according to Claim 1 or 2, characterised by the fact that the said teeth in the said second set are formed on a key inserted inside a second axial groove on the said shaft, the said second key moving axially in re lation to the said shaft and being locked axially in relation to the said case.

4) - Device according to one of the foregoing Claims, cha racterised by the fact that the said manually-operated control means comprise a first rotary bushing, coaxial and integral with the said shaft and provided with an axial groove for the teeth in the said second set, the said first bushing being connected, by means of an essen tially spherical coupling, to a second bushing integral with a control rod turning round and moving in the direction of its own axis, perpendicular to that of the said shaft, the said axis being arranged in such a manner that axial traversing of the said rod controls rotation of the said shaft for gear selection, whereas rotation of the said rod controls axial traversing of the said shaft for engaging the said gear.

5) - Device according to one of the foregoing Claims, cha racterised by the fact that the said first and said second groove on the said shaft lie in the same diametrical plane on the said shaft and in diametrically opposed positions.

Drawing